As is known, numerous metrology systems are available today, which among other fields, also find application in the aerospace field.
In particular, metrology systems are known that enable determining the attitude and/or position of a satellite. Even more particularly, metrology systems are known that, given a pair of satellites, enable determining the mutual position and the mutual attitude between the two satellites.
Determination of the attitudes and positions of satellites is of particular importance in the case of satellite systems in which the satellites are in formation, i.e. in cases where control of the attitude and/or position of each satellite as a function of the attitude/position of the other satellites is envisaged.
In practice, given two satellites, determining the mutual attitude and the mutual position requires determining six degrees of freedom. In particular, assuming a first and a second reference system, respectively integral with a first and a second satellite and each formed by a respective set of three perpendicular axes, the mutual attitude and the mutual position between the first and the second reference system, and therefore between the first and the second satellite, can be expressed in terms of (linear) displacements and rotations (angles). Even more particularly, the mutual position of the second satellite with respect to the first satellite can be expressed by a set of three displacements; similarly, the mutual attitude of the second satellite with respect to the first satellite can be expressed by a set of three angles.
That having been said, projective optical metrology systems are such that, given two satellites, one of them is equipped with a target formed by a number N of light sources, and the other satellite is equipped with an optical unit, which includes an optoelectronic sensor capable of acquiring an image of the target, on the basis of which, by means of post-processing, the optical unit determines one or more of the above-mentioned degrees of freedom.
By way of example, patent application EP1986018 discloses a system for determining the position and orientation of a system with six degrees of freedom, where the number N of light sources of the target is equal to one. However, to enable the determination of all six degrees of freedom, the system disclosed in EP1986018 requires that the sole light source is formed by a source of coherent light, for example, a laser, and also requires that the optical unit, in addition to processing the images of the target, is capable of taking measurements of the power effectively received by the optoelectronic sensor and a rotation angular measurement of polarization of the light beam emitted by the coherent light source. The system disclosed in EP1986018 therefore requires that both satellites have suitable optoelectronic circuits and a respective power supply.
On the other hand, metrology systems are known that do not contemplate determination of the power measurement, i.e. metrology systems of a purely projective type. An example of these metrology systems is provided in U.S. Pat. No. 7,561,262, where the light sources are formed by reflectors designed to be arranged on the second satellite, and which are illuminated by radiation emitted by the first satellite. In particular, referring to the transceiving unit and to the reflecting unit to indicate the portions of the metrology system described in U.S. Pat. No. 7,561,262 and arranged on the first and on the second satellite, respectively, this metrology system makes use of a passive-type reflecting unit. Therefore, the second satellite does not need any optoelectronic circuit, or a corresponding power supply, with a consequent reduction in energy consumption.
Although the metrology system described in U.S. Pat. No. 7,561,262 is therefore characterized by a relative constructional simplicity and reduced consumption, it contemplates that the transceiving unit, which equips the first satellite, emits an optical beam having a spatial distribution such as to effectively impinge on all the reflectors that equip the second satellite. Therefore, the optical beam is characterized by a cross-section of significant dimensions; consequently, the transceiving unit requires a significant amount of electric power in order to generate the optical beam.
Patent application US2003/071996 describes an optical metrology system that subdivides wideband radiation into a multiplicity of narrow-band subbands; each subband is associated with a subband optical system able to optimize performance regarding the range of wavelengths covered by the subband. In addition, the radiation of each subband is directed onto a detector, which generates corresponding electrical signals that can be processed by a processing unit.
U.S. Pat. No. 4,740,951 describes an integrated optical demultiplexer that is able to separate a plurality of monochromatic components forming a light beam that propagates in an input optical fibre; in addition, the demultiplexer is able to convey the thus-separated components to a plurality of output optical fibres.
U.S. Pat. No. 6,072,633 describes an apparatus able to generate, given an optical beam at input, three optical beams at output, having different colours. The apparatus comprises a pair of dichroic mirrors, a high-reflectivity wideband mirror and a gaseous material, which is interposed between the wideband mirror and the second dichroic mirror.